子串在數據幀R

Question

我已經從GPS日誌這樣的數據：（此數據在數據幀的列的行）

{"mAccuracy":20.0,"mAltitude":0.0,"mBearing":0.0,"mElapsedRealtimeNanos":21677339000000,"mExtras":{"networkLocationSource":"cached","networkLocationType":"wifi","noGPSLocation":{"mAccuracy":20.0,"mAltitude":0.0,"mBearing":0.0,"mElapsedRealtimeNanos":21677339000000,"mHasAccuracy":true,"mHasAltitude":false,"mHasBearing":false,"mHasSpeed":false,"mIsFromMockProvider":false,"mLatitude":35.1811956,"mLongitude":126.9104909,"mProvider":"network","mSpeed":0.0,"mTime":1402801381486},"travelState":"stationary"},"mHasAccuracy":true,"mHasAltitude":false,"mHasBearing":false,"mHasSpeed":false,"mIsFromMockProvider":false,"mLatitude":35.1811956,"mLongitude":126.9104909,"mProvider":"network","mSpeed":0.0,"mTime":1402801381486,"timestamp":1402801665.512} 

問題是我只需要緯度和經度值，所以我認爲可以使用substring和sappy來應用於數據框中的所有數據。

但我不確定這種方式很帥，因爲當我使用子字符串ex：substr("abcdef", 2, 4)，所以我需要從開始到「mLatitude」計算出多少個字符，所以任何人都可以給出建議快速處理它的方法？

謝謝@mnel回答的問題，它的工作，但我仍然有問題

從MNEL答案我已經創建功能是這樣的：

fgps <- function(x) { 
    out <- fromJSON(x) 
    c(out$mExtras$noGPSLocation$mLatitude, 
     out$mExtras$noGPSLocation$mLongitude) 
} 

，然後這是我的數據：

gpsdata <- head(dfallgps[,4],2) 

[1] "{\"mAccuracy\":23.128,\"mAltitude\":0.0,\"mBearing\":0.0,\"mElapsedRealtimeNanos\":76437488000000,\"mExtras\":{\"networkLocationSource\":\"cached\",\"networkLocationType\":\"wifi\",\"noGPSLocation\":{\"mAccuracy\":23.128,\"mAltitude\":0.0,\"mBearing\":0.0,\"mElapsedRealtimeNanos\":76437488000000,\"mHasAccuracy\":true,\"mHasAltitude\":false,\"mHasBearing\":false,\"mHasSpeed\":false,\"mIsFromMockProvider\":false,\"mLatitude\":35.1779956,\"mLongitude\":126.9089661,\"mProvider\":\"network\",\"mSpeed\":0.0,\"mTime\":1402894224187},\"travelState\":\"stationary\"},\"mHasAccuracy\":true,\"mHasAltitude\":false,\"mHasBearing\":false,\"mHasSpeed\":false,\"mIsFromMockProvider\":false,\"mLatitude\":35.1779956,\"mLongitude\":126.9089661,\"mProvider\":\"network\",\"mSpeed\":0.0,\"mTime\":1402894224187,\"timestamp\":1402894517.425}" 
[2] "{\"mAccuracy\":1625.0,\"mAltitude\":0.0,\"mBearing\":0.0,\"mElapsedRealtimeNanos\":77069916000000,\"mExtras\":{\"networkLocationSource\":\"cached\",\"networkLocationType\":\"cell\",\"noGPSLocation\":{\"mAccuracy\":1625.0,\"mAltitude\":0.0,\"mBearing\":0.0,\"mElapsedRealtimeNanos\":77069916000000,\"mHasAccuracy\":true,\"mHasAltitude\":false,\"mHasBearing\":false,\"mHasSpeed\":false,\"mIsFromMockProvider\":false,\"mLatitude\":35.1811881,\"mLongitude\":126.9084072,\"mProvider\":\"network\",\"mSpeed\":0.0,\"mTime\":1402894857416},\"travelState\":\"stationary\"},\"mHasAccuracy\":true,\"mHasAltitude\":false,\"mHasBearing\":false,\"mHasSpeed\":false,\"mIsFromMockProvider\":false,\"mLatitude\":35.1811881,\"mLongitude\":126.9084072,\"mProvider\":\"network\",\"mSpeed\":0.0,\"mTime\":1402894857416,\"timestamp\":1402894857.519}" 

運行時，爲什麼數據仍顯示在結果中，而不僅僅是結果值。

sapply(gpsdata, function(gpsdata) fgps(gpsdata)) 




    {"mAccuracy":23.128,"mAltitude":0.0,"mBearing":0.0,"mElapsedRealtimeNanos":76437488000000,"mExtras":{"networkLocationSource":"cached","networkLocationType":"wifi","noGPSLocation":{"mAccuracy":23.128,"mAltitude":0.0,"mBearing":0.0,"mElapsedRealtimeNanos":76437488000000,"mHasAccuracy":true,"mHasAltitude":false,"mHasBearing":false,"mHasSpeed":false,"mIsFromMockProvider":false,"mLatitude":35.1779956,"mLongitude":126.9089661,"mProvider":"network","mSpeed":0.0,"mTime":1402894224187},"travelState":"stationary"},"mHasAccuracy":true,"mHasAltitude":false,"mHasBearing":false,"mHasSpeed":false,"mIsFromMockProvider":false,"mLatitude":35.1779956,"mLongitude":126.9089661,"mProvider":"network","mSpeed":0.0,"mTime":1402894224187,"timestamp":1402894517.425} 
[1,]                                                                                                                                                                                          35.178 
[2,]                                                                                                                                                                                          126.909 
    {"mAccuracy":1625.0,"mAltitude":0.0,"mBearing":0.0,"mElapsedRealtimeNanos":77069916000000,"mExtras":{"networkLocationSource":"cached","networkLocationType":"cell","noGPSLocation":{"mAccuracy":1625.0,"mAltitude":0.0,"mBearing":0.0,"mElapsedRealtimeNanos":77069916000000,"mHasAccuracy":true,"mHasAltitude":false,"mHasBearing":false,"mHasSpeed":false,"mIsFromMockProvider":false,"mLatitude":35.1811881,"mLongitude":126.9084072,"mProvider":"network","mSpeed":0.0,"mTime":1402894857416},"travelState":"stationary"},"mHasAccuracy":true,"mHasAltitude":false,"mHasBearing":false,"mHasSpeed":false,"mIsFromMockProvider":false,"mLatitude":35.1811881,"mLongitude":126.9084072,"mProvider":"network","mSpeed":0.0,"mTime":1402894857416,"timestamp":1402894857.519} 
[1,]                                                                                                                                                                                          35.18119 
[2,]                                                                                                                                                                                          126.90841 

我想要的結果是這樣的：

[1] 35.178 126.909  
[2] 35.18119 126.90841 

謝謝

Answer 1

這樣看來，你的數據是JSON格式。因此，請使用RJSONIO::fromJSON來讀取文件。

如：

txt <- "{\"mAccuracy\":20.0,\"mAltitude\":0.0,\"mBearing\":0.0,\"mElapsedRealtimeNanos\":21677339000000,\"mExtras\":{\"networkLocationSource\":\"cached\",\"networkLocationType\":\"wifi\",\"noGPSLocation\":{\"mAccuracy\":20.0,\"mAltitude\":0.0,\"mBearing\":0.0,\"mElapsedRealtimeNanos\":21677339000000,\"mHasAccuracy\":true,\"mHasAltitude\":false,\"mHasBearing\":false,\"mHasSpeed\":false,\"mIsFromMockProvider\":false,\"mLatitude\":35.1811956,\"mLongitude\":126.9104909,\"mProvider\":\"network\",\"mSpeed\":0.0,\"mTime\":1402801381486},\"travelState\":\"stationary\"},\"mHasAccuracy\":true,\"mHasAltitude\":false,\"mHasBearing\":false,\"mHasSpeed\":false,\"mIsFromMockProvider\":false,\"mLatitude\":35.1811956,\"mLongitude\":126.9104909,\"mProvider\":\"network\",\"mSpeed\":0.0,\"mTime\":1402801381486,\"timestamp\":1402801665.512}" 

然後過程：

library(RJSONIO) 
out <- fromJSON(txt) 
out$$mLongitude 
#[1] 126.9105 
out$mLatitude 
#[1] 35.1812 

# to process multiple values 

tt <- rep(txt,2) 

myData <- lapply(tt, fromJSON) 
latlong <- do.call(rbind,lapply(myData, `[` ,c('mLatitude','mLongitude'))) 
# or using rbind list 

library(data.table) 
latlong <- rbindlist(lapply(myData, `[` ,c('mLatitude','mLongitude')))