(完整word版)SAS-Base認(rèn)證考試(70真題+答案詳解)

1、SAS Base認(rèn)證考試 70 題SAS分多個(gè)認(rèn)證種類：base， advanced ， clinic 等，但大多需要先通過(guò)base 認(rèn)證。但凡這類商業(yè)組織提供的考證，基本都是題庫(kù)型，所以想考過(guò)難度并不大。對(duì)于只想拿SAS認(rèn)證的人，如果熟練掌握網(wǎng)上流傳甚廣的sas 真題 70 題，通過(guò)base 認(rèn)證基本就沒問(wèn)題。Q 11. The following SAS program is submitted: data WORK.TOTAL;set WORK.SALARY; by Department Gender;if First. then Payroll=0; Payroll+Wagerate;

2、if Last.; run;The SAS data set WORK.SALARY is currently ordered by Gender within Department. Which inserted code will accumulate subtotals for each Gender within Department? A. GenderB. DepartmentC. Gender Department D. Department Gender答案： A本題知識(shí)點(diǎn)：自動(dòng)變量在 SAS讀取數(shù)據(jù)時(shí)，在PDV 過(guò)程中會(huì)產(chǎn)生很多自動(dòng)變量，在輸出的數(shù)據(jù)集中是不可見的。FIRST

3、.VARIABLE：同一個(gè)BY變量（組），若新的變量值第一次出現(xiàn)時(shí)，其first.variable值為 1。LAST.VARIABLE：同一個(gè)BY 變量（組），若新的變量值最后一次出現(xiàn)時(shí)，其last.variable 值為 1。另外，在 BY 變量右面有多個(gè)變量時(shí)，先按第一個(gè)變量排序，若第一個(gè)變量的觀測(cè)存在重復(fù)時(shí)，才按第二個(gè)變量排序。Q 2Given the following raw data records in TEXTFILE.TXT:1-|-10-|-20-|-30John,FEB,13,25,14,27,FinalJohn,MAR,26,17,29,11,23,CurrentTin

4、a,FEB,15,18,12,13,FinalTina,MAR,29,14,19,27,20,CurrentThe following output is desired:Obs Name Month StatusWeek1 Week2Week3Week4 Week51JohnFEBFinal$13$25$14$27.2JohnMARCurrent$26$17$29$11$233TinaFEBFinal$15$18$12$13.4TinaMARCurrent$29$14$19$27$20Which SAS program correctly produces the desired outpu

5、t?A. data WORK.NUMBERS;length Name $ 4 Month $ 3 Status $ 7;infile TEXTFILE.TXT dsd;input Name $ Month $;if Month=FEB then input Week1 Week2 Week3 Week4 Status $;else if Month=MAR then input Week1 Week2 Week3 Week4 Week5 Status $;format Week1-Week5 dollar6.;run;proc print data=WORK.NUMBERS;run;B. da

6、ta WORK.NUMBERS;length Name $ 4 Month $ 3 Status $ 7;infile TEXTFILE.TXT dlm=, missover;input Name $ Month $;if Month=FEB then input Week1 Week2 Week3 Week4 Status $;else if Month=MAR then input Week1 Week2 Week3 Week4 Week5 Status $; format Week1-Week5 dollar6.;2run;proc print data=WORK.NUMBERS;run

7、;C. data WORK.NUMBERS;length Name $ 4 Month $ 3 Status $ 7;infile TEXTFILE.TXT dlm=,;input Name $ Month $ ;if Month=FEB then input Week1 Week2 Week3 Week4 Status $;else if Month=MAR then input Week1 Week2 Week3 Week4 Week5 Status $;format Week1-Week5 dollar6.;run;proc print data=WORK.NUMBERS;run;D.

8、data WORK.NUMBERS;length Name $ 4 Month $ 3 Status $ 7;infile TEXTFILE.TXT dsd ;input Name $ Month $;if Month=FEB then input Week1 Week2 Week3 Week4 Status $;else if Month=MAR then input Week1 Week2 Week3 Week4 Week5 Status $;format Week1-Week5 dollar6.;run;proc print data=WORK.NUMBERS;run;答案： C本題知識(shí)

9、點(diǎn)：INFILE 語(yǔ)句與指示器、 INFILE filespecification options;其中， filespecification用來(lái)定義文件, options 給出選擇項(xiàng) ;filespecification有以下三種形式:3 、 fileref( 文件標(biāo)志 ) 、 filename文件(名 ) 、 CARDS指明輸入的數(shù)據(jù)，緊跟著CARDS語(yǔ)句下列選擇項(xiàng)(options) 可以出現(xiàn)在INFILE 語(yǔ)句中 : 、 COLUMN=variable 或 COL=variable 定義一個(gè)變量, 其值是指針?biāo)诘漠?dāng)前列位置。 、 END=variable 定義一個(gè)變量, 作為文件結(jié)束的

10、標(biāo)志。 、 EOF=label 是一個(gè)語(yǔ)句標(biāo)號(hào), 當(dāng) INFILE 語(yǔ)句讀到文件末尾時(shí), 作為隱含的GOTO 語(yǔ)句的目標(biāo)。 、 LENGHT=variable 定義一個(gè)變量, 其值是當(dāng)前輸入數(shù)據(jù)行的長(zhǎng)度。 、 FIRSTOBS=linenumber 要求從指定的行開始讀取數(shù)據(jù), 而不是從文件的第一個(gè)記錄開始。 、 OBS=n 指定從一個(gè)順序輸入文件中讀取數(shù)據(jù)的最后一個(gè)行(即第 1第 n 行 )。一個(gè)觀察可能占n 行。 、 DLM= 若分隔符不是空格，則使用DLM=指定 、 DSD 忽略引號(hào)中數(shù)值的分隔符；自動(dòng)將字符數(shù)據(jù)中的引號(hào)去掉；將兩個(gè)相鄰分隔符視為缺失值處理。 、 MISSOVER阻止 I

11、NPUT 進(jìn)入下一行讀取，未賦值變量視為缺失值。 、 TRUNCOVER與 MISSOVER相似，但在COLUMN INPUT 或 FORMATTED INPUT中使用。比較 與 的區(qū)別： 用于 1 個(gè)數(shù)據(jù)行用多個(gè)input 語(yǔ)句讀取，停留到下一個(gè)INPUT 語(yǔ)句。 用于 1 個(gè)數(shù)據(jù)行含有多個(gè)觀測(cè)值讀取時(shí)，停留到下一個(gè)DATA 步。Q 3The following SAS program is submitted:data WORK.DATE_INFO;Day=01 ;Yr=1960 ;X=mdy(Day,01,Yr) ;run;What is the value of the variabl

12、e X?A. the numeric value 0B. the character value 01011960C. a missing value due to syntax errorsD. the step will not compile because of the character argument in the mdy function.4答案： A本題知識(shí)點(diǎn)：數(shù)據(jù)類型的自動(dòng)轉(zhuǎn)換在 SAS中，日期時(shí)間是以1960 年 1 月 1 日 0 時(shí) 0 分 0 秒作為起點(diǎn)的。因此，mdy(1,1,1960)=0 。若把日期時(shí)間表示為常數(shù)時(shí)，要使用相應(yīng)的格式，帶單或雙引號(hào)，在后面緊跟一

13、個(gè)D（日期）、T（時(shí)間）、DT（日期時(shí)間）。在本題中，日期函數(shù)的參數(shù)應(yīng)該是數(shù)值，若是字符串，會(huì)先嘗試字符串是否可以轉(zhuǎn)換為數(shù)值，這是自動(dòng)轉(zhuǎn)換。自動(dòng)轉(zhuǎn)換是指系統(tǒng)產(chǎn)生一個(gè)臨時(shí)的變量來(lái)完成賦值或運(yùn)算。當(dāng)自動(dòng)轉(zhuǎn)換發(fā)生時(shí)，會(huì)在LOG 窗口中給出提示。1）、字符型變量-數(shù)值型變量在下面的情況中，VarB 是一個(gè)字符型變量，其它是數(shù)字型變量。賦值于一個(gè)數(shù)字型變量，如：VarA=VarB;在算術(shù)運(yùn)算中使用，如：VarA=VarB+0;與一個(gè)數(shù)字型變量進(jìn)行比較，如：if VarB=VarA;在函數(shù)中，參數(shù)要求數(shù)字型變量，如：VarA=sum(VarB,0);2）、數(shù)值型變量-字符型變量在下面的情況中，VarB 是

14、一個(gè)數(shù)字型變量，其它是字符型變量。賦值于一個(gè)字符型變量，如：VarA=VarB;在與要求字符的運(yùn)算符一起使用，如：VarA=|VarB;在函數(shù)中，參數(shù)要求字符型變量，如：VarA=trim(VarB);Q 4The Excel workbook REGIONS.XLS contains the following four worksheets:EASTWESTNORTHSOUTHThe following program is submitted:libname MYXLS regions.xls;5Which PROC PRINT step correctly displays the N

15、ORTH worksheet?A. proc print data=MYXLS.NORTH;run;B. proc print data=MYXLS.NORTH$;run;C. proc print data=MYXLS.NORTHe;run;D. proc print data=MYXLS.NORTH$n;run;答案： D本題知識(shí)點(diǎn)：打印Excel 的某個(gè)工作表的數(shù)據(jù)WHAT IS THAT“ $”ARACTER?CHLooking at SAS Explorer it may be surprising that each dataset written to Excel appears

16、 twice, once with theexpected name and once with a trailing“ $”.Unlike a typical data source, data in an Excel spreadsheet need not be left and top aligned. For this Excel hasnamed ranges which allow data to be placed anywhere inside a spreadsheet. By default SAS reads and writes datafrom named rang

17、es on spreadsheets, but will also read spreadsheet data directly in the absence of a named range.When a new SAS dataset is created in an Excel library, SAS creates both a spreadsheet and a named range. Eachis given the same name, with thespreadsheet denoted by a trailing“ $”.In the example at right

18、CLASS is the named range created by the Excel engine and CLASS$ is the spreadsheetcreated by the Excel engine to hold the named range. Within SAS, the named range is referred to as Wrkbk.CLASS,and the spreadsheet is referenced using the name literal Wrkbk. CLASS$ n.SAS name literals are name tokens

19、written as strings within quotation marks, followed by the letter n. Nameliterals allow the use of special characters that are not otherwise allowed in SAS names , like the“Excel libname engine to distinguish worksheets from named ranges. For more information see the Recommended Readings.摘自 De-Mysti

20、fying the SAS LIBNAME Engine in Microsoft Excel: A Practical GuideQ 5Which statement specifies that records 1 through 10 are to be read from the raw data file customer.txt?A. infile customer.txt 1-10;B. input customer.txt stop10;C. infile customer.txt obs=10;D. input customer.txt stop=10;答案： C本題知識(shí)點(diǎn)：

21、INFILE 的選項(xiàng)FIRSTOBS=常數(shù)，要求從指定的行開始讀取數(shù)據(jù), 而不是從文件的第一個(gè)記錄開始。OBS=常數(shù)，指定從一個(gè)順序輸入文件中讀取數(shù)據(jù)的最后一個(gè)行(即第 1第 n 行 )。一個(gè)觀測(cè)可能占n 行。6Q 6After a SAS program is submitted, the following is written to the SAS log:101 data WORK.JANUARY;102 set WORK.ALLYEAR(keep=product month num_Sold Cost);103 if Month=Jan then output WORK.JANUAR

22、Y;104 Sales=Cost * Num_Sold;105 keep=Product Sales;-22ERROR 22-322: Syntax error, expecting one of the following: !,!, &, *, *, +, -, =, , =, , =,AND, EQ, GE, GT, IN, LE, LT, MAX, MIN, NE, NG, NL,NOTIN, OR, =, |, |, =.106 run;What changes should be made to the KEEP statement to correct the errors in

23、 the LOG?A. keep=(Product Sales);B. keep Product, Sales;C. keep=Product, Sales;D. keep Product Sales;答案： D本題知識(shí)點(diǎn)：KEEP語(yǔ)句與 KEEP=選項(xiàng)在處理大型數(shù)據(jù)集時(shí)，KEEP=選項(xiàng)的效率較高。KEEP語(yǔ)句： KEEP variable(s); 不能用于過(guò)程步。KEEP=選項(xiàng)： data-set-name( KEEP=variable(s) )可以用于數(shù)據(jù)步（如，DATA 語(yǔ)句、 SET語(yǔ)句）、過(guò)程步。其中， variable(s) 是具體變量，不能是數(shù)組、_N_、 _ERROR 等。Q

24、77Which of the following choices is an unacceptable ODS destination for producing output that can be viewed in Microsoft Excel?A. MSOFFICE2KB. EXCELXPC. CSVALLD. WINXP答案： D本題知識(shí)點(diǎn)：ODS 輸出Most of these destinations are designed to create output for viewing on a screen or for printing. The OUTPUT destina

25、tion creates SAS data sets. The MARKUP destination is a general purpose tool for creating output in formats defined by tagsets. This includes XML (eXtensible Markup Language), EXCELXP, LaTeX, CSV (comma-separated values), and many other formats where data can be thought of as separated by tags. The

26、DO CUMENT destination, on the other hand, allowsyou to create a reusable output “ document ” that yo u can rerender for any destination. So, if your boss decides he really wants that report in PDF, not RTF, you can replay the output documentwithout having to rerun the entire SAS program that created

27、 the data. With an output document, you can also rearrange, duplicate, or delete tables to further customize your output.摘自 The Little SAS Book (Fourth)P152 頁(yè)Q 8The SAS data set named WORK.SALARY contains 10 observations for each department, and is currently ordered by Department.The following SAS p

28、rogram is submitted:data WORK.TOTAL;set WORK.SALARY(keep=Department MonthlyWageRate);by Department;if First.Department=1 then Payroll=0;Payroll+(MonthlyWageRate*12);if Last.Department=1;run;Which statement is true?A. The by statement in the DATA step causes a syntax error.B. The statement Payroll+(M

29、onthlyWageRate*12); in the data step causes a syntax error.8C. The values of the variable Payroll represent the monthly total for each department in the WORK.SALARY data set.D. The values of the variable Payroll represent a monthly total for all values of WAGERATE in the WORK.SALARY data set.答案： C本題

30、知識(shí)點(diǎn)：類似第1 題Q 9data course;input exam;datalines;50.1;run;proc format;value score 1 50 = Fail51 100 = Pass ;run;proc report data =course nowd;column exam;define exam / display format=score.;run;What is the value for exam?A. FailB. PassC. 50.1D. No output答案： C本題知識(shí)點(diǎn)：PROC FORMAT語(yǔ)句PROC FORMAT;VALUE nameran

31、ge- 1= formatted-text- 1;range- 2= formatted-text- 2;range- n= formatted-text- n;9若 name 為字符串設(shè)計(jì)格式，則必須在開頭加$，長(zhǎng)度不超過(guò)32 字節(jié)；name 不能以數(shù)字結(jié)尾，除了下劃線外，不能含其他的任何特殊字符。在 range 右側(cè)文本可達(dá)到 32767 字節(jié)。變量值是字符串要加引號(hào)。range 是多個(gè)值，要用逗號(hào)。連續(xù)的要用 -。關(guān)鍵字 low 、 high 指代變量中最小和最大的非缺失值。用 排除或指代某些范圍。other 是給其他沒列在VALUE中的變量分配格式。Q 10The following

32、SAS program is submitted:data WORK.RETAIL;Cost=$20.000;Discount=.10*Cost;run;What is the result?A. The value of the variable Discount in the output data set is 2000. No messages are written to the SAS log.B. The value of the variable Discount in the output data set is 2000. A note that conversion ha

33、s taken place is written to the SAS log.C. The value of the variable Discount in the output data set is missing. A note in the SAS log refers to invalid numeric data.D. The variable Discount in the output data set is set to zero. No messages are written to the SAS log.答案： C本題知識(shí)點(diǎn)：標(biāo)準(zhǔn)數(shù)據(jù)、以及數(shù)據(jù)類型的自動(dòng)轉(zhuǎn)換非標(biāo)準(zhǔn)數(shù)

34、據(jù)含逗號(hào)的數(shù)值，如：1,00,001 ；包含美元符號(hào)、十六進(jìn)制、壓縮十進(jìn)制的數(shù)據(jù)；日期是最普通的非標(biāo)準(zhǔn)數(shù)據(jù)。標(biāo)準(zhǔn)數(shù)據(jù)10數(shù)字 0-9英文句號(hào)科學(xué)計(jì)數(shù)、 E+、 -如果字符型變量轉(zhuǎn)換后不能作為標(biāo)準(zhǔn)數(shù)值讀入，被轉(zhuǎn)換成的字符型變量有格式要求，必須進(jìn)行顯式轉(zhuǎn)換。Q 11Given the existing SAS program:proc format;value agegrplow-12 =Pre-Teen13-high = Teen;run;proc means data=SASHELP.CLASS;var Height;class Sex Age;format Age agegrp.;run;W

35、hich statement in the proc means step needs to be modified or added to generate the following results:Analysis Variable : HeightNSex AgeObsMinimumMaximumMean-FPre-Teen351.359.855.8Teen656.566.563.0MPre-Teen457.364.859.7Teen662.572.066.8-A. var Height / nobs min max mean maxdec=1;B. proc means data=S

36、ASHELP.CLASS maxdec=1 ;C. proc means data=SASHELP.CLASS min max mean maxdec=1;D. output nobs min max mean maxdec=1;答案： C本題知識(shí)點(diǎn)：PROC MEANS過(guò)程PROC MEANS ;語(yǔ)句 ;RUN;? data=：數(shù)據(jù)集maxdec=：指定輸出結(jié)果的小數(shù)位數(shù)，默認(rèn)為7 位noprint ：禁止結(jié)果在OTPUT 窗口輸出alpha：設(shè)定可信區(qū)間的水平，默認(rèn)為 0.05? MAX 、 MIN 、MEAN 、 MEDIAN 、 N 、 NMISS 、 RANGE 、 STDDEV 、

37、 SUM11若不加統(tǒng)計(jì)關(guān)鍵詞，默認(rèn)打印的順序：非缺失值個(gè)數(shù)（N ）、均值（ MEAN ）、標(biāo)準(zhǔn)差（STDDEV ）、最小值（MIN ）、最大值（MAX ）。? 語(yǔ)句若在 PROC MEAN過(guò)程中沒有其他語(yǔ)句，默認(rèn)輸出所有觀測(cè)值和所有數(shù)值變量的統(tǒng)計(jì)量。BY ：分變量單獨(dú)分析，數(shù)據(jù)必須先按變量順序排序，即PROC SORTCLASS ：分變量單獨(dú)分析，不用排序VAR ：指定使用的數(shù)值變量Q 12The Excel workbook QTR1.XLS contains thefollowing three worksheets:JANFEBMARWhich statement correctly a

38、ssigns a library reference to the Excel workbook?A. libname qtrdata qtr1.xls;B. libname qtr1.xls sheets=3;C. libname jan feb mar qtr1.xls;D. libname mydata qtr1.xls WORK.heets=(jan,feb,mar);答案： A本題知識(shí)點(diǎn)：LIBNAME語(yǔ)句格式LIBNAME libref SAS-data-library;Q 13The following SAS program is submitted:data WORK.TES

39、T;set WORK.MEASLES(keep=Janpt Febpt Marpt);array Diff3 Difcount1-Difcount3;array Patients3 Janpt Febpt Marpt;run;What new variables are created?A. Difcount1, Difcount2 and Difcount3B. Diff1, Diff2 and Diff3C. Janpt, Febpt, and MarptD. Patients1, Patients2 and Patients3答案： A本題知識(shí)點(diǎn)：數(shù)組與其他編程語(yǔ)言的數(shù)組相比不同在于，S

40、AS 數(shù)組的每個(gè)元素都對(duì)應(yīng)一個(gè)變量名。? 數(shù)值型數(shù)組數(shù)組說(shuō)明中的初始值可省略，默認(rèn)為缺失值。數(shù)組說(shuō)明中變量可省略，變量名默認(rèn)為數(shù)組名+ 序號(hào)。序號(hào)從 1 開始。ARRAY test(3)Math Chinese English (0,0,0);數(shù)組元素的個(gè)數(shù)由變量個(gè)數(shù)決定。ARRAY test(*) test3-test8;二維數(shù)組，數(shù)組元素按行排列。ARRAR x(2,2) x11 x12 x21 x22;? 字符型數(shù)組12字符型數(shù)組藥指定數(shù)組元素的最大長(zhǎng)度，其他與數(shù)值型數(shù)組相同。ARRAY test(2) $ 10 mathor father;? 臨時(shí)數(shù)組若 SAS 數(shù)組每個(gè)元素不對(duì)應(yīng)變量

41、名，即為臨時(shí)數(shù)組。這與其他編程語(yǔ)言相同。ARRAY test(3) _TEMPORARY_ (0,0,0);臨時(shí)數(shù)組只用于中間計(jì)算，不保存入數(shù)據(jù)集。在數(shù)據(jù)步中，臨時(shí)數(shù)組在數(shù)據(jù)步隱含循環(huán)中能自動(dòng)保留上一步得到的值。Q 14Which of the following programs correctly invokes the DATA Step Debugger:A. data WORK.TEST debug;set WORK.PILOTS;State=scan(cityState,2, );if State=NE then description=Central;run;B. data WO

42、RK.TEST debugger;set WORK.PILOTS;State=scan(cityState,2, );if State=NE then description=Central;run;C. data WORK.TEST / debug;set WORK.PILOTS;State=scan(cityState,2, );if State=NE then description=Central;run;D. data WORK.TEST / debugger;set WORK.PILOTS;State=scan(cityState,2, );if State=NE then des

43、cription=Central;run;答案： C本題知識(shí)點(diǎn)：/ debug 語(yǔ)法DEBUG 過(guò)程的調(diào)用方法：在DATA步后面增加DEBUG 選項(xiàng)。Q 15Which statement is true concerning the SAS automatic variable _ERROR_?A. It cannot be used in an if/then condition.B. It cannot be used in an assignment statement.C. It can be put into a keep statement or keep= option.D.

44、It is automatically dropped.答案： D本題知識(shí)點(diǎn)：自動(dòng)變量_ERROR_在 PDV 過(guò)程中，產(chǎn)生很多自動(dòng)變量，可以在數(shù)據(jù)步的表達(dá)式中使用，在輸出數(shù)據(jù)集中不可見。在 PDV 過(guò)程中， _N_ 、 _ERROR_ 默認(rèn)為 DROP 。在 KEEP 語(yǔ)句或 KEEP= 選項(xiàng)中，可以使用除了_N_ 、 _ERROR_ 之外的變量。Q 16The following SAS program is submitted:data WORK.DATE_INFO;X=04jul2005d;13DayOfMonth=day(x);MonthOfYear=month(x);Year=ye

45、ar(x);run;What types of variables are DayOfMonth, MonthOfYear, and Year?A. DayOfMonth, Year, and MonthOfYear are character.B. DayOfMonth, Year, and MonthOfYear are numeric.C. DayOfMonth and Year are numeric. MonthOfYear is character.D. DayOfMonth, Year, and MonthOfYear are date values.答案： B本題知識(shí)點(diǎn)：SAS

46、中日期時(shí)間及函數(shù)起點(diǎn)： 1960年1月 1日 0時(shí) 0分0秒。若將日期時(shí)間標(biāo)示為數(shù)值型常數(shù)，需使用相應(yīng)格式。格式值帶單引號(hào)，后跟一個(gè)D（日期）、T （時(shí)間）、 DT （日期時(shí)間）。日期函數(shù)返回值為數(shù)值。Q 17Given the following data step:data WORK.GEO;infile datalines;input City $20.;if City=Tulsa thenState=OK;Region=Central;if City=Los Angeles thenState=CA;Region=Western;datalines;TulsaLos AngelesBa

47、ngor;run;After data step execution, what will data set WORK.GEO contain?A. CityStateRegion-TulsaOKWesternLos AngelesCAWesternBangorWesternB. CityStateRegion-TulsaOKWesternLos AngelesCAWesternBangorC. CityStateRegion-TulsaOKCentralLos AngelesCAWesternBangorWesternD. CityStateRegion-TulsaOKCentralLosC

48、AWesternBangor14答案： A本題知識(shí)點(diǎn)：IF語(yǔ)句若執(zhí)行語(yǔ)句不能在一個(gè)語(yǔ)句完成，則使用復(fù)合語(yǔ)句DO 和 ENDIF 條件 THEN 語(yǔ)句 ;沒有 ENDIF ，沒有IF-ELSEIF-ELSE多分支結(jié)構(gòu) ,語(yǔ)句 1 只能是一個(gè)語(yǔ)句。IF 條件 THEN 語(yǔ)句 1;；Q 18Which statement describes a characteristic of the SAS automatic variable _ERROR_?A. The _ERROR_ variable maintains a count of the number of data errors in a DATA step.B. The _ERROR_ variable is added to the program data vector and becomes part of the data set being created.C. The _ERROR_ variable can be used in expressions in